Since hydraulic fluid will inherently seek the flow path of least resistance, implements composed of hinged or flexibly connected frames, or implements having rigid frames with non-uniform loading, which are raised and lowered by hydraulic rams connected in parallel usually will not remain level as their elevation is changed. Prior art attempts to overcome this problem have generally concentrated on the use of master-slave arrangements connected in series. However, master-slave arrangements require special cylinders, the necessary structure of which is often not consistent with what is generally regarded as good hydraulic design practice. Specifically, the seal of the piston must pass over an orifice, which is not desirable as it tends to accelerate wear on the seal. In addition, the tolerances normally encountered in manufacture can cause plastic or permanent deformation in the implement frame due to the excess stroking required to achieve rephasing. The master-slave arrangement also amounts to a closed system and all air must be bled from that system for it to function properly. Bleeding such a system is often a troublesome and time consuming chore.
It is, therefore, an object of this invention to provide a level lift system for an agricultural implement which is capable of utilizing conventional hydraulic rams, which is less likely to cause distortion or deformation of the implement frame, and which minimizes the necessity for bleeding the hydraulic system with which it is associated.
It is also an object of this invention to provide a level lift system in which rephasing occurs automatically without the need for any one of the cylinders to go to the limit of its stroke.